This invention is related in general to the field of digital audio signal processing. More particularly, the invention is related to a digital graphic equalizer control system and method.
A graphic equalizer is a piece of audio equipment used to flatten the system spectral response in the audio signal band or produce other desirable effects. Current mid- to high performance audio systems typically include an analog graphic equalizer. Although analog systems produce excellent sound, there is a steady migration to digital systems. Digital systems are less costly to manufacture, are easy and flexible to modify, are programmable, and are portable. Further, the source of the audio signal is increasingly more likely to be digital than analog.
A graphic equalizer is made up of a set of equalizing filters with fixed center frequencies and bandwidths. Usually these filters are designed to span the entire audio band. The user is provided the capability to adjust the gain of these filters to change the equalization characteristics of the audio system and thus the output sound.
When a user alters the gain of the various equalizing filters in a digital graphic equalizer, undesirable artifacts discernible by the human ear are often generated because of the discrete, discontinuity nature of digital adjustment. These audible artifacts may sound like pops, clicks, zipper noises and swooshing noises. Typical techniques to minimize these artifacts are generally too costly, impracticable, and/or ineffective. For example, it was thought that by changing the equalizing filter coefficients in much smaller increments, such as 0.01 dB steps, the artifacts would be eliminated. However, 0.01 dB steps require an unacceptably large number of settings, such as 3,600 settings for a +/xe2x88x9218 dB audio control range. The large number of settings require additional implementation time, increase in programming complexity, and added costs of increased memory size.
Accordingly, there is a need for a digital graphic equalizer control system and method that substantially eliminates artifacts as equalizing filter coefficients are changed.
In one aspect of the invention, a digital graphic equalizer uses a predetermined number of equalizing bands each having a different center frequency, and the center frequencies span a predetermined audio bandwidth. For each equalizing band a minimum set of filters is provided. The filters have a predetermined linear uniform spacing between the gain of successive filters.
In another aspect of the invention, a method of digital graphic equalizer control includes the steps of receiving a user-selected gain setting for a equalizing filter, and gradually increasing or decreasing the filter gain in uniform steps on a linear scale, then a final step of less than the uniform step size is used to reach the user-selected again setting.
In yet another aspect of the invention, a digital audio system includes a digital graphic equalizer having a predetermined number of equalizing bands each having a different center frequency. The center frequencies of the bands span a predetermined audio bandwidth. Each equalizing band includes a minimum set of filters with a predetermined uniform linear spacing between the gain of successive filters.
Technical advantages of the present invention includes the provision of digital graphic equalizer control that yields an artifact-free sound when the gain of the graphic equalizer is being adjusted. The sound quality is therefore much improved and vastly more enjoyable. Further, the present invention achieves the elimination of audible artifacts in an efficient manner without requiring large memory capacity or resource-intensive computations. Therefore, cost savings and small physical size are additional benefits of graphic equalizers employing the teachings of the present invention.